Extensive efforts have been made to provide flame retardant carpets for both residential and commercial buildings. A material currently used to provide flame retardancy in such materials is alumina trihydrate (Al.sub.2 O, 3H.sub.2 O), also known as hydrated alumina or ATH. Alumina trihydrate provides excellent flame retarding properties and is also non-toxic.
The alumina trihydrates used for this purpose are usually obtained by the extensive refining of natural bauxite. They are characterized by high purity and are substantially uniform in chemical characteristics. Obviously, this high degree of purity adds to the cost of the ATH product.
Heretofore, bauxite, a source of the refined alumina trihydrate, has not been found suitable as a flame retarding agent for such applications. The problem is that bauxites do not have uniform chemical and physical characteristics, and their appearance and composition will vary from geographical location to geographical location and may even differ from mining site to mining site within one location. A further problem is that grinding bauxite for use in filler applications typically produces considerably more fines than grinding ATH and these excessive fines can cause viscosity and processing problems. Nevertheless, interest continues in seeking ways to utilize bauxites as flame retardant fillers.
U.S. Pat. No. 4,216,130 of Rigge et al., issued Aug. 5, 1983, teaches that bauxite can be rendered compatible with carpet backing polymer compositions if it is processed so as to have an alumina (Al.sub.2 O.sub.3) content of from about 40% to about 60% by weight wherein the Al.sub.2 O.sub.3 is in hydrated form, with the balance being Fe.sub.2 O.sub.3, TiO.sub.2 and SiO.sub.2 and other impurities, and the bauxite must be ground so as to have a surface area of less than 12 m.sup.2 /g when dried for one hour at 100.degree. C., have a pH of at least 6.5 measured at 20.degree. C. in an aqueous suspension containing 5 grams of ground bauxite/100 grams of water, and a particle size distribution wherein the particles of less than about 3 microns in size constitute less than about 15% by weight of the ground bauxite.
However, these property ranges are rather restrictive and accordingly there still remains a need to provide a formulation package and bauxite particle size specification to cover a wider range by which bauxites may be used as flame retardant fillers in polymer compositions used in carpet backings.